[linux-lvm] Is it possible to invalidate snapshots other than by overfilling?

[Jonathan Brassow]

It sounds like the module needed by device-mapper to support snapshots  
is not loaded when it is needed.  (Perhaps the module - dm-snapshot -  
is not in your initrd image?)

After step 3, but before step 4, try doing a 'dmsetup table' to see if  
things are properly mapped.  A 'dmsetup status' wouldn't hurt either...

Certainly, there should never be a kernel oops...  It's tough for me  
to say whether this bug is already fixed - given the age of your kernel.

  brassow

On Jul 1, 2008, at 4:10 PM, Rob West wrote:

> Does anyone know of ways that snapshots can become invalid other  
> than by writing more to the origin than the COW device can hold?
>
> The reason I ask is that we're having cases where a snapshot is  
> becoming invalid, but we are very skeptical that it is due to  
> overfilling. The size of the origin is 83G, and the size of the  
> snapshot is 8G.
>
> Here's what little we can tell from the logs:
> 1. Backup script creates a snapshot and starts copying data from it.
> 2. Before backup is finished (and thus, snapshot removed), the user  
> reboots.
> 3. On reboot, we get the following message which seems to be normal  
> for this kernel:
>     kernel: device-mapper: table: 253:2: snapshot-origin: unknown  
> target type
> 4. About 23 hours later, the backup script tries to create the  
> snapshot again but fails b/c it's still there.
> 5. The backup script tries to clean up by removing the snapshot, but  
> lvremove causes a kernel oops because the snapshot is invalid. (We  
> have identified a potential patch for this, but are trying to figure  
> out why the snapshot was invalid in the first place.)
>
> The kernel we're using is based off of Fedora 6 (2.6.18-1.2849).
>
> Not sure whether it matters, but device-mapper is version 1.02.07  
> release 4.0.RHEL4 and lvm2 is version 2.02.06 release 6.0.RHEL4.
>
>
> Thanks for any help,
> Rob
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